The present invention relates generally to a synchronous control system for rotary printing presses, and more particularly to a synchronous control system for rotary printing presses in which driving means for independently driving a plurality of printing units and a folding unit for cutting and folding a printed paper web into predetermined printed images, and control sections for controlling the driving means for driving the printing units are provided; at least one printing unit having a direct web path running from the printing unit in question to the folding unit and a detour web path running from the printing unit in question to the folding unit via other printing units; the synchronous control system is effective at printing on the paper web passed through the detour web path in such a manner that printing images are changed while the web is being transported by changing over the printing units through which the paper web is passed, and is capable of overprinting on the paper web passed through the detour web path by simultaneously operating the printing units through which the web is passed.
The aforementioned rotary printing press, which is a rotary printing press comprising a plurality of printing units and a folding unit for cutting and folding a printed paper web into predetermined printing images; each of the printing and folding units being driven separately by an independent driving means; each of the printing units having a direct web path running from the printing unit in question directly to the folding unit and a detour web path running from the printing unit to the folding unit via other printing units; the rotary printing press capable of printing on the paper web passed through the detour web path in such a manner that printing images are changed while the web is being transported by changing over the printing units through which the web is passed, is disclosed in Japanese Published Unexamined Patent Application No. Hei-8(1996)-207233.
Japanese Published Unexamined Patent Application No. Hei-8(1996)-207233, however, discloses only a rough outline of the control of the rotary printing press, but not in detail. In particular, there is no mention in the document of preliminary measures to cope with changes in the length of a paper web path from the printing position to the cutting and folding position before and after the changeover of the printing units.
In a rotary printing press having a plurality of printing units and a folding unit for cutting and folding the printed paper web into predetermined printing images, each of the units driven separately by independent driving means, reference points are provided on the printing cylinder of the printing unit and the rotating cylinder of the folding unit so that when the printing and folding units are rotated, the reference points of both cylinders are in synchronism with each other to obtain a reference rotating phase that is a predetermined rotating phase. Based on the reference rotating phase thus obtained, the rotating speed and the rotating phases of both cylinders are caused to agree with each other. As a result, when the paper web is passed on a particular web path where the length up to the cutting position of the folding unit is a predetermined length, the position at which the printing image printed by the printing unit is to be cut agrees with the position at which the folding unit cuts the paper web.
For this reason, changes in the length of the web path from the printing position to the cutting position on the folding unit before and after the changeover of the printing units cause a shift in the position of the cutting line with respect to a predetermined printing image. This has often produced defective prints (waste) in the conventional type of rotary printing press.
To prevent this, there has been proposed a method where the reference rotating phase of the printing cylinder, particularly the plate cylinder, as a driven section of the printing unit is determined in accordance with the length from the printing position of the printing unit to the cutting position of the folding unit for each paper web path so that the printing cylinder of the printing unit being changed over is driven at a reference rotating phase suitable for the paper web path in question.
Each printing unit, however, has a specific reference rotating phase for a typical direct web path through which the paper web is usually passed directly to the folding unit. It is therefore not practical to preset a reference rotating phase for each paper web path because of the need for a large number of reference rotating phases. Furthermore, designating a necessary reference rotating phase could lead to mistakes in selection.
Setting a reference rotating phase for several detour web paths running by way of other printing units could increase the risk of mistakes in selection since a larger number of reference rotating phases might be required in some cases where a number of direct web paths for other printing units are set as branches in the downstream side.
Even when a reference rotating phase is set for the printing cylinder of each printing unit to match a relatively longer path from the printing position of the printing unit to the cutting position of the folding unit, the differences in the elongation of travelling paper webs resulting from differences in the physical properties, such as Young""s modulus, of paper webs used could lead to a significant difference in elongation as accumulated in the paper web path up to the cutting position of the folding unit. This could cause a shift in the position of cutting lines in cutting predetermined printing images on the web. In the conventional type of rotary printing press, it has been necessary, therefore, to correct the shift by operating an adjust roller device provided in the downstream of the paper web path and in the upstream of the folding unit.
With the aforementioned method, the differences in the elongation of paper webs used resulting from differences in the physical properties thereof could lead to a significant difference at the cutting position in the folding unit even when there are no mistakes in selecting the reference rotating phase, not to speak of cases where there have committed mistakes in selecting the reference rotating phase. This could cause a shift in the position of cutting lines for cutting printing images, involving corrective operations. Furthermore, a large amount of defective prints could be produced even during these corrective operations.
The present invention has been conceived taking into account these problems. In a rotary printing press comprising a plurality of printing units and a folding unit for cutting and folding a printed paper web into predetermined printing images, the object of the present invention is to prevent waste when printing is carried out, by changing printing images while the paper web, which is passed through a detour web path from one printing unit to the folding unit via the other printing units, is kept travelling by changing over the printing units through which the paper web is passed.
It is another object of the present invention to make it possible to overprint printing images on a paper web, which is passed through a detour web path from one of the printing unit to the folding unit via the other printers, by simultaneously operating the printing units through which the paper web is passed.
To achieve the above objectives, the present invention is characterized in that in a synchronous control system for a rotary printing press in which driving means for independently driving a plurality of printing units and a folding unit for cutting and folding a printed paper web into predetermined printing images are provided, and control sections for controlling the driving means for each unit are provided; at least one printing unit having a direct web path from the printing unit to the folding unit, and a detour web path to the folding unit via the other printing units,
the control section of a printing unit having a detour web path comprises
a phase correction value output section for generating a phase correction value on the basis of the length of a path between the printing unit in question and another printing unit in the detour web path,
a signal output section for generating an appropriate signal representing a drive reference speed on the basis of a given drive reference, and a signal output section for generating an appropriate signal representing a drive reference phase, and
a signal output section for generating an appropriate signal representing a feedback speed on the basis of a given feedback signal, and a signal output section for generating an appropriate signal representing a corrected phase obtained by correcting the feedback speed on the basis of the feedback signal with a phase correction value,
a control signal is generated by correcting a drive reference speed signal with a signal relating to the difference between the drive reference phase and the corrected phase and a feedback speed signal, and
the drive of the printing unit is controlled by the control signal.
When printing is made on a paper web passed through a detour web path by changing printing images by changing over a plurality of printing units through which the web is passed, or when printing images are overprinted on a paper web passed through a detour web path by simultaneously operating a plurality of printing units through which the paper web is passed, the present invention having the aforementioned construction exercises control in such a manner that the rotating phase of the driven part of a printing unit in the upstream side of the detour web path is in agreement with, and in synchronism with, the reference rotating phase of the driven part of the printing unit at a position at which the paper web leaving the printing unit directly reaches the folding unit.
With this control, the positions of printing images to be printed by a plurality of printing units through which the paper web is passed agree with each other. Consequently, when printing images are changed by changing over the printing units, no shift is caused in the positions of cutting lines for cutting the printing images even after the printing units are changed since the printing image after change is printed at a position at which the printing image before change would have been printed.